Fabrication of Multi-Functional Sintered Materials with Graded Compositional Distribution

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A laser beam differential temperature heating test and a hydrogen/oxygen burner flame heating test were made on the graded specimens of metal and ceramics, fabricated under the design scheme established in the forgoing two years. An acoustic emission monitoring was used to detect the crack formation in the specimen during heating and cooling cycle. Vertical cracks were observed to be formed during cooling cycle of testings. The vertical cracks propagated by further heating and cooling, and they eventually coalesce to result in the spallation of the ceramic layr from specimen surface. Finite element analysis on the stress state in the specimen was done using the measured temperature distribution, and it has shown that a large compressive stress is generated during heating period at the ceramic surface to cause non-elastic deformation of the ceramic layr. The non-elastic deformation will cause during cooling peiod tensile stress, which will exceed the intrinsic strength of the ceramics and result in the formation of the vertical cracks. From the microstructural observations of the crack propagation in the composite structures consisted of metal and ceramic phase the improvement of the ductility of the ceramic-rich regions has been found to be indispensible for the retention of the heat resisrtance of this kind of functionally gradient materials. Such an improvement will be realized by an control of the connectivity of the metal phase in the ceramic-rich region through a process optimization. The heat insulating performance is evaluated by thermal resistance of the material, and its value is a characteristic parameter, along with the heating temperature of the vertical crack formation, for the thermomechanical performance of functionally gradient materials. The concept of the microstructual control of graded materials, particulary with respect to the connectivity of the phases involved, will be applied to the other kind of functionally gradient materials, such as ther